1. Field of the Invention
The present invention relates to an electrodepositing solution and an electrodeposition method using the same, which are to be used in forming a color filter suitable for various indicating elements and color image sensors or to be used in electrodeposition coating. More particularly, the invention is concerned with an electrodepositing solution capable of being electrodeposited at a low potential in accordance with an electrodeposition method or a photoelectrodeposition method, as well as an electrodeposition method using the electrodepositing solution.
2. Description of the Related Art
At present, as color filter fabricating methods there are known (1) a dyeing method, (2) a pigment dispersing method, (3) a printing method, (4) an ink jet method, and (5) an electrodeposition method. These methods have respective peculiar characteristics and advantages, but involve the following drawbacks.
The dyeing method taken up first requires a photolithographic process for patterning; in addition, light resistance is poor because a dye is used, and the number of manufacturing steps is large.
The pigment dispersing method taken up second also requires a photolithographic process for patterning, and the number of manufacturing steps is large, resulting in high cost.
The printing method taken up third and the ink jet method taken up fourth do not require a photolithographic process, but the former is inferior in point of resolution and the uniformity of film thickness and the latter is apt to cause mixing of colors and is inferior in point of resolution and positional accuracy.
The electrodeposition method taken up fifth requires a patterning process by photolithography such as formation of a pre-patterned electrode and therefore the pattern shape is limited; in addition, a high voltage of 70V or higher is needed. Thus, this electrodeposition method is not applicable to a liquid crystal provided with a thin film transistor (TFT). According to this electrodeposition method, for example in the case of electrodeposition coating, a film having a certain degree of thickness can be formed usually by the supply of a high voltage in the range from 100V to 200V. However, when a high voltage is applied, excess protons are fed around an electrode and a dehydrogenation reaction proceeds rapidly, with the result that there occurs what is called a bubbling phenomenon in which oxygen is produced as bubbles by the dehydrogenation reaction. In this case, there occurs a problem such that the film formed separates from the bubble-generated surface of the electrode and becomes a non-smooth film containing voids or a film having defects.
Generally, in the case of a color filter for liquid crystal, with only formation of a color filter layer, the filter is not employable. It is necessary that filter cells of different colors be covered with a black matrix. Usually, a photolithographic method is adopted also for forming the black matrix, which is one of principal causes of an increase of cost.
In view of the abovementioned points and taking note of a compound which is soluble in water and which becomes less soluble or dispersible in an aqueous liquid as the pH changes, the inventors in the present case have proposed a technique of fabricating a color filter in accordance with a photoelectrodeposition method (Japanese Published Unexamined Patent Application Nos. Hei 11-133224 and Hei 11-174790). According to this proposed technique, an organic or inorganic semiconductor is utilized as a substrate and is irradiated with light in a pattern form, causing the pH of a semiconductor interface in an aqueous solution to change partially, whereby a desired pattern film can be formed by deposition. It is not necessary to adopt a photolithographic process, nor is it necessary to apply a high voltage. Thus, this technique can cope with even a complicated pixel pattern of a high definition. In addition, it is easy to form a black matrix and there can be made a great contribution to the reduction of cost of a color filter.
However, even when the above photoelectrodeposition method is adopted, for a system wherein a photovoltage based on a photosemiconductor does not reach a threshold voltage required for electrodeposition, a bias voltage is applied for an auxiliary purpose from the standpoint of stably forming an electrodeposition film having a more uniform thickness and color density and having a smooth surface. But from the standpoint of reducing the number of manufacturing steps and simplifying the equipment structure, it is desired to develop a technique not requiring the application of a bias voltage and capable of forming a high quality electrodeposition film with use of light alone.
On the other hand, if a high quality electrodeposition film can be formed even by the application of a low voltage alone, there are attained simplification of the equipment structure and reduction in the number of manufacturing steps and of cost. Without being badly influenced by the application of a high voltage, it is possible to make a further improvement in quality of the film formed.
For example, in the case of electrodeposition coating not based on the above photoelectrodeposition method, a voltage as high as several hundred volts has heretofore been applied taking into account, for example, film loss caused by re-dissolving in a solution after the application of voltage has been stopped. For the application of such a high voltage, however, a power supply of a large capacity is needed. There has also been the problem that the deterioration of the solution is accelerated due to dissolving-out of metal ions from the material to be film-deposited which material is a metal. Moreover, as noted earlier, the film quality is deteriorated by the bubbling phenomenon. Further, when viewed from the standpoint of a working environment, the application of a high voltage is dangerous.
In the case where a TFT substrate with conductive films (electrodes) and thin film transistors (TFTs) arrayed thereon is used as a material to be film-deposited, if an electrodeposited film (color filter film) having a uniform thickness, a uniform color density and a smooth surface can be formed stably by utilizing only a driving voltage for a TFT without forming a photosemiconductor on the electrodes, the foregoing deterioration of the solution used and deterioration of the film quality caused by the bubbling phenomenon are prevented and it is possible to attain the simplification of equipment and the reduction of cost.
Thus, there has not been provided yet a way for stably forming an electrodeposited film having a uniform thickness, a uniform color density and a smooth surface free of concaves and convexes by the application of a low voltage in accordance with the electrodeposition method or photoelectrodeposition method.
The present invention has been accomplished in view of the abovementioned circumstances and solves the abovementioned problems involved in the related art.
The present invention provides an electrodepositing solution for low-potential electrodeposition for use in an electrodeposition method and a photoelectrodeposition method, capable of improving the film formability under the application of a low voltage, suppressing the elution of metal ions, and further capable of stably forming an electrodeposition film having a uniform thickness, a uniform color density and a smooth surface.
The present invention also provides an electrodeposition method utilizing the electrodeposition method and the photoelectrodeposition method, superior in film formability under the application of a low voltage, and capable of suppressing the elution of metal ions and stably forming by deposition an electrodeposition film having a uniform thickness, a uniform color density and a smooth surface.
More specifically, according to one aspect of the present invention, for solving the foregoing problems, there is provided an electrodepositing solution for low-potential electrodeposition, capable of forming by deposition an electrodeposition film of an electrodeposition material on an electrically conductive (simply xe2x80x9cconductivexe2x80x9d hereinafter) material upon application of a voltage between the conductive material and a counter electrode, the electrodeposition material containing an electropositive polymer material, at least one component of which is a copolymer containing a hydrophobic monomer, a hydrophilic monomer and a plastic monomer.
Preferably, the conductive material is either a substrate having a light-transmissible conductive film on a light-transmissible base or a substrate with light-transmissible conductive films arrayed on a light-transmissible base.
In another aspect of the present invention there is provided an electrodeposition method wherein, with a conductive material contacted with an aqueous electrodepositing solution, a voltage is applied between a conductive material and a counter electrode disposed in an electrodepositing solution while allowing the conductive material to be contacted with the water electrodepositing solution, to form by deposition an electrodeposition film of an electrodeposition material on the conductive material.
Preferably, the conductive material is either a substrate having a light-transmissible conductive film on a light-transmissible base or a substrate with light-transmissible conductive films arrayed on a light-transmissible base.
In a further aspect of the present invention there is provided an electrodepositing solution for low-potential electrodeposition which permits an electrodeposition film of an electrodeposition material to be formed by deposition of a Conductive material upon application of a voltage between the conductive material and a counter electrode, the electrodeposition material exhibiting a hysteresis characteristic as a deposition characteristic for the applied voltage and containing a plastic component.
In a still further aspect of the present invention there is provided a color filter having as a color film an electrodeposited thin film of a copolymer, which contains a hydrophobic monomer, a hydrophilic monomer and a plastic monomer.
In a still further aspect of the present invention there is provided a filter provided with a transparent substrate, a transparent conductive film formed on the transparent substrate, a photosemiconductor film formed on the transparent conductive film and a color film formed by a copolymer on the photosemiconductor film, the copolymer containing a hydrophobic monomer, a hydrophilic monomer and a plastic monomer.